This invention relates to methods of generating gases and more particularly to methods of generating hydrogen gas.
Acceleration of projectiles launched from gun, rocket, and missile systems is limited by the sonic velocity of gas products from propellants. Conventional gun propellants (nitrocellulose) generate heavy gases like carbon dioxide, carbon monoxide, nitrogen oxide, and water vapor whose sonic velocity seldom exceeds 500 m/sec at ambient temperature. The maximum speed of projectiles launched from gun barrel by such gases barely reaches 1 km/sec.
Hydrogen gas which outspeeds any other gases (under same pressure and temperature), owing to its low molecular weight, is an ideal fluid to impart its kinetic energy efficiently to a projectile. For this reason hydrogen gas is used in a two-stage gas gun (1) that launches a projectile to hypervelocity (over 6 km/sec). This type of gun is operated by a two step process. In the first stage, gun powder charge is ignited to drive a piston against hydrogen gas stored in a gas reservoir. In the next stage, the rise of hydrogen gas pressure due to the compression eventually actuates a valve mechanism at the base of the launch barrel and pressurized hydrogen is released to push a projectile. Besides this multi-staged pressurization, the whole operation of the device also includes storing of the gas nearby and mechanisms for its transfer to the reservoir. Although the staged gas gun routinely increases the projectile velocity up to 7 km/sec, the complexity of the operation makes it cumbersome and impractical for routine uses.
Hydrogen gas can be generated chemically in such reactions as decomposition of metal hydrides or oxidation of metal like aluminum by water. When metal hydride is mixed with a certain metal oxide, the decomposition of the hydride is greatly accelerated and the overall reaction accompanies a net energy gain. However, the amount of heat and gas generated per unit mass or volume of the reactants in the decomposition is not clearly advantageous over conventional propellants. Energetically, the reaction of aluminum with water is more favorable than combustion of the propellants. However, due to the formulation of passive oxide film on the metal surface, the oxidation reaction is never sustained unless the temperature of the metal is raised above the melting point of its oxide. Therefore, such metallic systems need to be activated energetically in order to generate hydrogen gas which is clearly more energetic than the gases from the conventional propellants, or to complete the hydrogen generating reaction.
Woodrow W. Lee and Richard D. Ford in U.S. Patent Application Ser. No. 07/199,879 filed on May 27, 1988 and titled, "Method for Launching Projectiles with Hydrogen Gas," disclose a method in which a high power pulse of electrical current is applied to a metal fuel element made of aluminum, an aluminum-lithium alloy, or an aluminummagnesium alloy in the form of a wire or a foil causing the metal fuel element to explode dispersing a mixture of vaporized and molten metal into water surrounding the metal fuel element. The dispersed fine metal particles react with the water generating hydrogen gas at high pressure. After the metal fuel element has exploded, the electrical current is continued in order to drive the reaction between the metal and water. After a preselected hydrogen pressure is achieved, the hydrogen gas is used to propel a projectile from a barrel.
The Lee et al. method described above has some drawbacks. First, energization (melting, vaporization and dispersion) of aluminum wire for its reaction with the surrounding water solely depends on electrical energy. Thus, it is a energy demanding process--about 10 KJ of electrical energy for 1 gm of aluminum. Second, the volume of water used in the above case is in far excess the stoichiometric amount in order to contain and to have surface contact with the exploded metal. This results in vaporization of the excess water that mixes with the hydrogen product gas to increase its weight.